The present invention relates to a method for detecting fetal Edwards syndrome (Trisomy 18) during prenatal screening. More particularly the present invention relates to a method for improving detection efficiency in screening for Edwards syndrome by measuring the amount of the free beta subunit of human chorionic gonadotropin (hCG) in the blood of pregnant women.
Edwards syndrome, also referred to as trisomy 18, is a cause of severe mental retardation. Generally, fetal Edwards syndrome can be determined by a diagnostic procedure including amniocentesis and karyotyping. However, this diagnostic procedure is invasive and involves risk to the woman and the fetus. Amniocentesis and karyotyping are not routinely performed during all pregnancies. Instead, one or more screening methods may be utilized to determine when the risk to the pregnancy warrants the risk of undergoing an invasive diagnostic procedure.
Historically, the prenatal search for chromosomal abnormalities has focused on pregnant women at and over the age of 35, at which age the risks of chromosomal abnormalities in the fetus approach or exceed the risks of diagnostic procedures utilized to detect fetal chromosomal abnormalities. Therefore the standard method of prenatal screening has involved selecting women for diagnostic amniocentesis on the basis of maternal age. Age, however, is an inadequate screening criterion in that only about 5% of all Edwards syndrome pregnancies can be detected by carrying out amniocentesis and karyotyping on the 5% of pregnant women most at risk, that is, those aged 35 years or greater. And, because in actual clinical practice only about half of the women aged 35 years or greater undergo amniocentesis and karyotyping, fewer than 2.5% of Edwards syndrome pregnancies are prenatally detected.
I have discovered a previously unknown association between lowered levels of maternal blood free beta-hCG and fetal Edwards syndrome. A screening method using the maternal blood level of free beta hCG will vastly improve the detection efficiency of Edwards syndrome. Detection efficiency refers to the percentage of cases of fetal Edwards syndrome which are correctly detected for a chosen cut off level. The cut off level will be more fully explained in a following section. These and other discoveries will be more fully explained in the Summary of the Invention section and the Detailed Description of the Invention section.
One object of the present invention is to provide a method and process for screening for fetal Edwards syndrome which detects a greater percentage of fetal Edwards syndrome cases for a given false positive rate than other known prenatal screening methods.
Another object of the present invention is to provide a method and process for screening for fetal Edwards syndrome which has a lesser false positive rate for a given detection percentage than other known methods.
A still further object of the present invention is to provide a method and process for screening for fetal Edwards syndrome by measuring the level of maternal blood free beta-hCG.
Other objects and advantages of the present invention will become apparent in the following description of the invention.